Apparatus for molding plastic material



Nov. 28, 1950 M.E.NYE ETAL APPARATUS FOR MOLDING PLASTIC MATERIAL FiledDec. 4, 1948 2 Sheets-Sheet 1 n A.- A-..

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Nov. 28, 1950 M. E. NYE ETAL 2,531,888

APPARATUS FOR MOLDING PLASTIC MATERIAL Filed Dec. 4, 1948 2 Sheets-Sheet2 Patented Nov. 28, 1950 APPARATUS FOR MOLDING PLASTIC MATERIAL MauriceE. Nye and Harry E. Nye, Barberton, Ohio, assignors to The Nye RubberCompany, a corporation of Ohio Application December 41948, Serial N0.63,458

5 Claims. l

This invention relates to apparatus for molding plastic material and isof especial advantage in the molding and vulcanizing of small rubberarticles such, for example, as rubber toy wheels which are chosen forthe purpose of illustration herein.

When molded in an ordinary two-part mold, by forcing the two moldsections toward each other with an excess of rubber between them toprovide high pressure upon the rubebr in the mold cavities, the excessof rubber prevents the two mold sections from coming all the waytogether and results in mold ns on the product which are required to beremoved, and, especially in the case of very small articles, the cost ofremoving the mold ns is an undesirably large percentage of the totalcost of the product.

Further, in the case of a plastic material such as a rubber compositioncontaining a comminute filler, the resistance to flow in a narrowpassage is not merely a direct, simple ratio to the distance of flow,but accords to some type of mathematical progression, resistanceincreasing static pressure and static pressure increasing resistance.Therefore, lling an intricate mold cavity from one or two major openingsrequires very high pressure and temperature, and for that reason alonemany molding devices now in use are very dicult to operate, and producemuch scrap.

A further problem little understood and dicult to remedy is trapped airin the mold cavities of a rubber mold. Scrap results when trapped airbecomes compressed and prohibits the rubber or other plastic fromfilling out the entire cavity.

Therefore, an object of this invention is to reduce the cost of moldedarticles by avoiding the forming of a large mold fin on the article.

Another object of this invention is to provide molded articles with onlysuch light mold ns at any position thereon that they will beunobjectionable or can be removed inexpensively by a tumbling operation,or light buling.

Another object of this invention is to provide a maximum rubber supplyfor mass action at the beginning of the molding step, and a minimum ofscrap per molded article at the vend of the molding step.

A still further object of this invention is to provide an improved feedfor a plastic molding assembly, said feed eliminating elaborate andexpensive injection mechanism.

Yet another object of the invention is to feed a rubber compound intothe molding chambers throughhighly restricted passageways in a mold 2assembly in order that the rubber compound will be evenly heatedthroughout and thereby have an even consistency without cold viscousportions, and equally ll all portions of the molding chambers.

Another object of the invention is to provide molding plates havingfilling gates therethrough, wherein the openings into the "lling gatescover a large portion of the surface of the plate and provide lateralanchorage for a slab of rubber compound pressed toward the surface.

A still further object of the invention is to provide lling gates intothe molding chamber, the gates having a progressively smallercrosssectional area, whereby a funneling action is accomplished toincrease the pressure and improve the flow of the compound through thegates into the molding chamber.

AnotherV object of the invention is to feed rubber compound in thinsheet form into a molding chamber, the thin sheet form placing therubber in intimate contact with the molding plates for thoroughpreheating.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims, taken in conjunctionwith the accompanying drawings, in which:

Figure 1 is a plan View of a mold plate having mold cavitiesconstituting half a mold chamber for toy wheels, and embodying andadapted for the practice of the invention in its preferred form;

Figure 2 is a plan view of a mold plate having mold cavitiesconstituting half a mold chamber for toy wheels, and having fillinggates therein;

Figure 3 is a plan view of a mold plate having mold cavitiesconstituting half a mold chamber for toy wheels, and having lling gatestherein;

Figure 4 is a plan view of a mold plate having mold cavitiesconstituting half a mold chamber for toy wheels;

Figure 5 is a top plan View of a mold assembly using two mold couples,the first mold couple comprising the plates of Figures 1 and 2, and thesecond mold couple comprising the plates of Figures 3 and 4;

Figure 6 is a section of the mold assembly of Figure 5 along line 6 6;

Figure 7 is a section of the mold assembly of Figure 5 along line 1 1;

Figure 8 is an enlarged portion of the plate of Figure l illustratingone arrangement of radiating grooves adapted to conduct owable plastic`into the mold chamber;

.,30 may be seen in the Figure 14.

Figure 9 is a modification of the arrangement of the radiating grooves;

Figure 10 is still another modification of the arrangement of theradiating grooves;

Figure 11 is an exploded perspective View of the mold assembly of Figure5, and including a slab of uncured rubber compound in the properrelative position with respect to the mold couples;

Figure 12 is a broken-away section of the mold assembly taken along aline indicated by the line 5 5 on the one plate of the assemblyillustrated in Figure 8, the slab of uncured rubber being shown in itsposition relative to the mold couples at the instant of the beginning ofthe molding operation;

Figure 13 is a view similar to Figure 12 at the end of the moldingoperation;

Figure 14 is a broken-away section along the line I4--I4 of Figure 12;and

Figure l5 is a portion of Figure 13 in the area of one fillingy gate andmolding chamber, enlarged to emphasize the extreme small cross-sectionalarea of the feeder tubes relative to the molding chamber.

This application can best be understood by -f referring to the relativeposition of the parts in Figure 4, but describing and illustrating the iparts individually and in enlarged detail. It is to :be understood thatmolding plates for toy auto- -mobile wheels are being illustrated by wayof f .section, is indicated by reference character I0.

In the illustrated embodiment, the mold plate section I0 is a steelplate having a contact surface 33. The contact surface 33 is formed withcavities Il, each cavity being adapted to mold half of the externalsurface of a Wheel. In the floor -of each cavity Il is mounted a centralmolding i core or pin I2 adapted to -mold an internal axle opening inthe wheel.

Another, or top mold plate section, is illustrated A in Figure 2 and isreferredY to as the second mold 4plate section. The second mold platesection is indicated by reference character I3. The plate y section I3has an external surface 3| and a con- The contact surface of the tactsurface 32.

second mold plate section I3 is formed with cavities I4, each adapted tomold the other half of the external surface of the wheel. The cavitiesII and I4 together define a molding chamber 20. The cavities II and I4on the first and second .mold plate sections IIJ and I3 are aligned bymeans of dowel pins I6 with contact surfaces 33 and 32 thereof incontact with one another. The rst and second mold plate sections, whenmated together, constitute a molding couple.

In every molding operation Whether it is casting of iron, molding ofrubber, or any other type, there is always the twin problem of fillingthe molding chamber and removing the excess stock after molding. Theseproblems are much more Ainvolved than they may appear to the average`-inechanic who has never faced the problem.

In Figure 7 of the drawing, which is an enlarged portion of plate IB ofFigure 1, very small groove recesses 311 are illustrated extending fromeach of the mold cavities I to another cavity I4. The extremely smalldimension of the recesses In Figure 2, ythe mold plate I3 is shown withfilling gates I5 extending therethrough from the external surface 3| tothe contact surface 32. The filling gates I5 are tapered and extend, asillustrated in the Figures 12, 13 and 14, from the external surface 3ito the contact surface 32. The filling gates I5 are positioned tocoincide with the groove recesses 30 in the plate I0. Therefore, asillustrated in Figures 12 and 13, the filling gates I5 and the grooverecesses 3e provide a continuous passageway from the external surface:SI of the plate I3 into the molding chamber defined by the cavities IIand I4.

The molding plates I0 and I3 as described constitute a molding couple.The plates I and I3 may be preliminarily assembled in face-to-facerelation with the contact surface 32 of plate I3 in contact with thecontact surface 33 of plate I. Dowel pins It accurately align thecavities IIl and i4 with. respect to one another, as well as theopenings of the filling gates I5, with respect to the groove recesses35. This molding couple is a complete unit in itself and may be used byplacing a slab ofv uncured rubber compound in contact with theA externalsurface SI of plate I3 and pressing the slab of rubber compound towardthe external surface 3i in a heated press. The slab of rubber compoundwill become more plastic under heat, and may be forced into the fillinggates I5 and through the groove recesses 3ninto the molding chambers.

As the rubber compound passes through the groove recesses 3G it flows invery small ribbon cross section, and therefore is in intimate co'ntactwith the hot mold plates. The rubber compound is thereby uniformlyheated. Further, as illustrated best in Figures 14 and l5, the grooverecesses 30' are in the order of about .0010 inch deep andare preferablyas Wide as the small end opening of the iilling gates, although in someinstances they may be Wider, and may be as much as 1722 inch deep. Inother words, the groove recesses 353- when capped by the` mating platesection, arev very small and highly restricted' passageways bearing ahigh ratio with respect to the area of the small end of the gates.Preferably, the larger the filling gate the larger the ratio, but

:- in most instances the ratio should preferably remain about 1:10. Thisratio has the effect of greatly increasing the velocity of flow throughthe groove' recesses with respect to the flow through the filling gates,and helps to ll the molding chamber smoothly and evenly.

Figuresy 9 and 10 of the drawings illustrate two alternative methods ofproviding the groove recesses in the face of the molding plate l0. Inthe Figure 8, the recesses extend in straight lines between the variouscavities Ill, and a lling gate is adapted to terminate substantially inthe center of each recess between two particular cavities I4.rIherefore, each filling gate is adapted to provide a iiow of rubbercompound into two adjacent mold cavities Ill, and on the other hand eachcavity Iii has the advantage of being served by a plurality of recesses36 entering at radial points around the periphery thereof. In someinstances, the illustrated dual function of one filling gate is not themost desirable, and therefore a plurality of individual radiatinggrooves 30 as illustrated in Figure 9 may be provided. The mold plate I3must then be provided with filling gates to coincide With each of thevindividual radiating recesses. In Figure l0, a further alternative isprovided in which one lling gate enters through the mold plate I3 at acommon junction of three groove recesses 30 and thereby serves threeindividual cavities. The principle of operation of the three illustratedalternatives is subchambers.

5 stantially the same, and other modifications may readily be providedwithin the scope and purpose of this invention.

The preferred embodiment of this invention employs a double-deck unit oftwo molding couples and thereby permits the use of a large slab ofrubber without undue waste, because two sets of molding chambers must befilled and therefore a large slab of rubber 25 can be placed between themolding couples at the start of the molding process and yet only aminimum amount of scrap will remain at the end of the molding process.Figures 3 and 4 illustrate the individual mold plates I8 and I9 whichconstitute a second molding couple which is substantially the exactoperative equivalent of the rst molding couple.

.The Figures l2 and 13 illustrate in cross section, the entire moldingapparatus as comprising the described rst molding couple including moldplate sections l5 and I3, and the second molding couple including moldplate sections I8 and I9. The plate section E8 corresponds exactly tothe plate section l El of the first molding couple in an invertedposition, and the plate section I9 correspo-nds exactly to the platesection I3 in an inverted position. In other words, insofar as thefundamental features and operation are concerned, the second moldingcouple is exactly the same as the rst molding coup-le in an invertedposition. As a matter of fact, the assembly as illustrated may be turnedover and the first molding couple would then be the inverted couple. Ifthe assembly were inverted, the operation of the filling gates andrecesses, the anchor effect of the plurality yof filling gates, land allother features and operations of the invention would re- -main andoperate.

The Figures 12 and 13 illustrate the relative position cf the rst andsecond molding couples before the molding process is begun and after themolding process has finished. A slab of unvulcanized rubber 25 is placedbetween the molding couples as illustrated, and heat and pressure areapplied to the. molding couples to force the uncured rubber through thegates I5 and groove recesses 3o into the molding chambers 20, and causea curing action to cure the. rubber in` the molded form. The slab 25 canbe relatively large because of the double-deck construction of thisimpro-ved molding assembly, without unduly wasting the rubber asvulcanized scrap. In other words, there is a definite amount of rubber'required to lill the molding chambers 2B and the recesses 39 and llinggates l5. In addition to that lamount of rubber required, an excess ofrubber must be used to prevent the forcing means from contacting theexternal face of the plate section. The excess is required because aconstant pressure must be maintained upon the rubber unt-il it isentirely cured within the molding If the forcing means is permitted tocontact the external tace of the plate section, then the pressure willnot bey properly maintained within the m-olding chamber,

Furthermore, for a reason not fully understood by the applicant, a largemass of rubber provides some sort of mass action which tends to forcemore rubber compound into the lling gates I5 than can be conducted bythe groove recesses Se. .The tapered form of the gates I5 also aids infunneling an excess of rubber in attempting to force the excess into thegroove recesses 3B. The combined effect of the large mass action withlthe tapered form of the filling gates I5 and the increased velocitybecause of the small ratio size of the groove recesses 3l) assurescomplete lllng of the molding chambers without entrapped air. Figure 13illustrates the relative position of the molding coup-les, and therelative thickness of the scrap at the end of the molding process. It isplainly seen that the amount of scrap is considerably less per moldingchamber than could possibly be obtained by a single molding couple.

The two plate sections of each couple being very smoothly and accuratelyfaced and preliminarily assembled in face-to-face relation, the twocouples of mold sections: are adapted to be forced v to-ward each otherregardless of whether only one molding chamber 20, or several chambersare to be filled. Thus, two important functions are provided with thesame construction:

(l) When the press rst begins to close, the unvulcanized rubber slab 25is pressed lightly and portions thereof sink into the various gates I5.Because of this preliminary indenting effect, the sheet of stock isfirmly interlocked with the external faces of the second mold platesections, and each small localized area behaves like a separate piece ofsto-ck. Very little side movement is experienced tending to force therubber out between the two molding couples. There is some such tendency,of course, and an excess thickness of sheeted stock is provided toassure filling the molding chambers, but thisslight excess is easilycontrolled.

(2) The mold chamber lls better and pro-'- duces fewer pieces of scrapcaused by entrapped air in the mold. The reason why such a plurality ofsmall feeder tubes to provide multiple feeding has proven so successfulis not fully understood, but several years experience with molds havingonly one entry, and the improvement noted in recent months with theimproved mold disclosed herein, has provided ample proof that a distinctimprovement has resulted. The described mass action and excess stockundoubtedly are contributing factors, as well as the iilling of themolding chambers from opposing sides thereof, and the increased velocityproduced by the small groove recesses 30.

In the operation of the apparatus, the lower mold couples, comprisingplates I0 and I3, are assembled in close ttingface-to-face relationship,with cavities lI and I4 held in proper registration by the dowels orpins I6. A sheet or slab 25 of unvulcanized rubber composition is laidupon the external face SI of plate member I3. The upper mold couples,comprising plates I8 and I9, are assembled in like manner and arebrought down upon the sheet of rubber. See Figure 11. In actualconstruction of the preferred embodiment of this invention, in which thetwo molding couples are used in inverted relationship as illustrated,end guards 22 and 23 are attached to the plates I9 and I3 respectivelyand serve to help restrain iiow of the rubber composition .from betweenthe two mold couples. Furthermore, end guards 22 and 23 serve tosubstantially align the recesses of the lling gates I5. After the upperand lower mold couples are assembled, the assembly is placed in avulcanizing platen press, and the press .is closed upon the assembly toforce the rubber composition to flow into the gates I5 and fill themolding chambers. The assembly is then held in the press for asuflicient length of time to effect vulcanization of the rubber, thepressure being released and re-applied from time to time if desired, lasin the practice sometimes employed in the case of'ordinary molds topermit air or gas to escape and to assure complete ll- .ing of the moldcavities.

After vulcanization is completed, as illustrated in Figure 13, the pressis opened, the assembly is removed from the press if the type of pressis such as to require it, and the mold couples are separated and thefinished wheels and the scrap rubber between the two mold couples areremoved.

In this part of the operation the preferred procedure is to irstseparate the top and bottom mold plates i and I3 from the plates I3 andI9 and thereby withdraw the molding pins from the wheels. Suchsepa-ration is aided by notches 24 in plates I8 and I8 into which a prybar may be inserted. The integral relation of the wheels to the scraprubber at the ends of the grooves causes the wheels to be retained inthe cavities of the two plates I3 and i9, and thereby permits the pinsI2 to be withdrawn from the molded articles in one simple action. Theconstruction of the mold to provide suiiicient integral connectionbetween the scrap in the filling gates with the finished article to thusretain the finished article, is a feature of this invention which makesthe structure operative and highly desirable for mass production.. Ifthe molded articles were not retained in the cavities ifi, then theywould have to be individually withdrawn oif of the pins l2 in thecavities II.

Therefore, the scrap remaining between the plates I 3 and i9 and withinthe filling gates I5 and grooves 38, serves the very desirable functionof uniting all of the molded articles in one integral unit and thereforepermits the pins I2 to be withdrawn from the finished article.

The two plates i3 and I9 are then forced apart to break the thin annularwebs of rubber connecting the scrap in the iilling gates I5 with thescrap in groove recesses 3Q leading to the wheels of one or the other ofthe plates i3 and 5s, after which the web of scrap is pulled free fromthe wheels in the other plate. That is, plates 3 and I9 are forced apartby pry-bar action, and, of course, the scrap remaining between the moldcouples has only a limited flexibility and therefore will tear away fromthe scrap in groove recesses 3G leading to wheels in one or the other ofthe plates. Thereafter, the operator may grasp the web of scrap and peelit from the external surface 3l of the other plate and rupture the bondbetween the scrap in the gates l5 and the scrap in the groove recesses3B in the remaining plate. Thus, the finished wheels are left in thecavities of the plates i3 and i3, but are completely separated from thescrap and the pins I2,

except for very fine annular ns which are easily removed.

-The nnished wheels, substantialiy without mold fins, are then punchedfromy the cavities in which they have been retained, preferably by meansof a gang punch or other suitable removing means.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way oi' exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

l. Molding apparatus comprising, a iirst molding couple, said coupleincluding a iirst mold section having a contact surface with at least amold cavity extending inwardly of the said section from the said contactsurface, a second mold section having a contact surface with at least amold cavity extending inwardly of the said section from the said contactsurface, said second mold plate having a back surface, one of said moldsections having a plurality oi" groove recesses each radiating outwardlyfrom said at least a mold cavity therein, said second mold sectionhaving a plurality of filling gates opening through the plate from theback surface thereof and each registering with one said groove recess,said contact surfaces of the first and second mold sections beingadapted to contact in close fitting engagement and position the saidmold cavities of the first and second mold sections in registration todeiine a molding chamber, and cover the radiating groove recesses todefine closed feeder tubes from said iilling gates to said mold chamber,and means for pressing a piece of sheeted plastic flatwise against saidback surface to cause the plastic to flow through said plurality offilling gates into the mold cavity, said means comprising a secondmolding couple having substantially the characteristics defined for saidfirst molding couple, whereby said rst and second molding couplesthereby are movable toward one another to squeeze a sheet of iiowablematerial therebetween and force the material into all said filling gatesand feeder tubes simultaneously to iill the chambers.

2. Molding apparatus comprising, a first and a second molding couple,each molding couple including a first mold plate section having acontact surface dening a flat plane, said iirst mold plate sectionhaving at least a mold cavity extending inwardly thereof from the saidcontact surface, and each said molding couple including a second moldplate section having a contact surface deiining a fiat plane, saidsecond mold plate section having at least a mold cavity extendinginwardly thereof from the said contact surface, at least one of saidplate sections in each couple having a plurality of groove recesses eachradiating outwardly from said cavity therein, said second mold platehaving a back surface and having a plurality of filling gates eachhaving a large opening through the second mold plate from the said backsurface to a small opening at the contact surface, said contact surfacesof the i'irst and second mold plate sections being removably positionedin close fitting engagement with said mold cavities in registrationdeiining at least a molding chamber, said radiating groove recessesdening feeder tubes from said small openings of the filling gates tosaid at least a molding chamber, said first and second molding couplesbeing removably positioned together with the said back surfaces of therespective second mold plates movable toward one another to squeeze asheet of ilowabie material therebetween and force the material into al1said lling gates and feeder tubes simultaneously to iill said at least achamber in each molding couple, and means to resist escape of saidfiowable material from between said back surfaces.

3. Molding apparatus comprising, a iirst and a second molding couple,cach molding couple including mold plates adapted tc be preliminarilymated in close fitting contact to `dei'ine a plurality of moldingchambers with a plurality of radiating feeder tubes extending therefrom,each tube of each chamber extending to a terminus, said terminus alsobeing the terminus for a tube extending from another chamber, one ofsaid mold plates being formed with a multiplicity of iilling gates eachextending from an external face thereof through said plate to one saidterminus, said rst and second molding couples being removably positionedwith the said external faces thereof movable toward one another tosqueeze a sheet oi uncured rubber compound therebetween, whereby saidsheet of uncured rubber may be intially interlocked with said externalfaces by pressing a portion from said sheet into each said filling gateopening and thereby resist side movement of the sheet in the plane ofsaid external face, and may thereafter be further squeezed to force therubber compound into each filling gate and through said feeder tubesinto said molding chambers.

4. Molding apparatus comprising a pair of mold sections adapted to bemated in close-fitting relation to define a mold cavity, one of saidsections being formed with a filling aperture extending from an externalface thereof to said cavity, means for so pressing a piece of sheetedplastic iiatwise against said external face as to cause the plastic toiiow through said lling aperture into the mold cavity, said meanscomprising a second pair of mold sections having substantially thecharacteristics just dened as to the first pair, and guard means on asection of at least one of the pairs for resisting escape of plasticfrom between the two pairs of mold sections.

5. Molding apparatus comprising a pair of mold sections adapted to bemated in close-fitting relation to define a mold cavity, one of saidsections being formed with a lling aperture extending from an externalface thereof to said cavity, means for so pressing a piece of sheetedplastic flatwise against said external face as to cause the plastic toflow through said filling aperture into the mold cavity, said meanscomprising a second pair of mold sections having substantially thecharacteristics just dened as to the rst pair, and means for resistingescape of plastic from between the two pairs of mold sections.

MAURICE E. NYE. HARRY E. NYE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,919,534 Shaw July 25, 19331,997,074 Novotny Apr. 9, 1935 2,043,584 Husted June 9, 1936 2,072,349Wayne Mar. 2, 1937 2,452,382 Long Oct. 26, 1948

